Robert F. Foster

Texture and surface roughness of PRCVD aluminum films

Abstract The effects of temperature, substrate type and diluent gas flow trajectories on the film growth rate, surface roughness, crystal orientation, average grain size, and grain size uniformity of tri-isobutyl aluminum (TIBA) sourced CVD aluminum films were studied. Films were deposited in a lamp heated, single wafer, cold wall reactor using several process sequences which included variations on temperature ramping, precursor flow rate, and diluent gas flow. For 30-s depositions on TiN coated Si(111) substrates, pulsing the precursor flow for 5 s at the start of temperature ramp down from 673 K followed by deposition for 25 s at 573 K resulted in films with higher nucleation densities and larger fractions of Al(111) texturing, in addition to lower surface roughnesses and smaller grain sizes, when compared to films deposited at 573 K constant temperature. For 10-min depositions using four different temperature protocols, the type of substrate had a significant effect on the fraction of Al(111) texturing. The films deposited during temperature ramp down from 673 to 573 K with 10-s pulses at the start of deposition had higher Al(111) texturing and lower surface roughness than films deposited during the other process trajectories for all four different substrates. The estimated relative median time between electromigration failure (MTBF) is two to three times higher for the films deposited using a 10-s pulse during ramp down from either 673 or 623 K on PVD TiN coated Si(100) substrates as compared to other process protocols on the different substrates. During the programmed substrate temperature ramp down from 673 to 573 K, introducing 25 sccm diluent gas into the reactor at 573 K resulted in films with higher growth rates, larger average grain sizes and higher Al(111) fractions when compared to films deposited without diluent gas. However, introducing 75 or 100 sccm diluent gas resulted in films with lower growth rates, smaller average grain sizes, lower grain size variances and higher Al(111) fractions when compared to films deposited without diluent gas.

The Effects of Temperature Ramping on MOCVD Al Film Properties

We present and discuss experiments designed to demonstrate the effects of ramping substrate temperature during the deposition of TIBA sourced aluminum on Si(100) and TiN x coated silicon (TiN) wafers. We also present results from experiments in which the precursor flow was pulsed (started and stopped) for a short time at a higher temperature followed by temperature ramp down and deposition at a lower (constant) temperature on TiN wafers. Aluminum growth rates and crystal orientation data are presented for different deposition conditions on Si(100) wafers. Aluminum nucleation densities, crystal orientation, average grain size, surface roughness, growth rate and resistivity data are presented for different deposition conditions on TiN wafers. During substrate temperature ramp down from 673 K on TiN wafers, when the precursor flow was pulsed for a short time at higher temperatures, and then resumed at a lower (constant) temperature 573 K, there was a significant increase in both deposition rates and fraction of (111) orientation. The resistivities of these films were close to that of bulk aluminum. Films deposited during substrate temperature ramp down on TiN substrates resulted in higher fractions of (111) oriention and higher resistivities as compared to the films deposited at constant substrate temperature and during the ramp up of substrate temperature. The films deposited on Si(100) wafers during substrate temperature ramp down from 673 K to 573 K had strong Al(200) orientation.